H IGGS PRODUCTION AT R UN 2 AND PROJECTIONS FOR THE HL-LHC WITH THE CMS PHASE -2 DETECTOR Alessandro Da Rold, on behalf of the CMS Collaboration Interpreting the LHC Run 2 data and Beyond Trieste, 27 - 31 May 2019
O VERVIEW ‣ Run 2 ‣ H → 𝜐𝜐 @ 13 TeV ‣ HH → bb 𝛿𝛿 @ 13 TeV ‣ Not in this talk ‣ HL-LHC ‣ ECAL @ Run 2 ‣ ECAL @ HL-LHC ‣ H → 𝛿𝛿 @ 13 TeV ‣ H → 𝛿𝛿 ‣ H → ZZ @ 13 TeV ‣ H → 𝜐𝜐 , HH → bb 𝛿𝛿 Details in Federico’s talk! � 2
ECAL DURING R UN 2 ‣ Hermetic, homogenous calorimeter placed inside solenoid magnet ➞ Barrel and endcaps configuration Endcap Preshower ‣ 75 000 lead tungstate ( PbWO 4 ) crystals: fast scintillation, radiation resistant, short radiation length ‣ Purposes: ‣ Precise measurement of electron and photon energies Barrel ‣ Precise time measurement (background rejection, particle identification ) ‣ Energy resolution and particle identification fundamental in the discovery and characterisation of the Higgs boson � 3
Phys. Lett. B 779 (2018) 283 ‣ Selection H → 𝜐𝜐 ‣ µ 𝜐 h , e 𝜐 h , eµ, 𝜐 h 𝜐 h ‣ Leptons must have opposite charge ‣ Fundamental to establish fermion masses generation mechanism ‣ High p Tmiss and small M TW , b-tag ‣ All decays studied exploiting ECAL information on number of deposits (1-prong, 1-prong + π 0 (s), 3-prongs) ‣ Categories ‣ Main backgrounds: Z → 𝜐𝜐 , W+jets, QCD (control ‣ 0-jet: H from gluon fusion sample), tt (simulation) ‣ VBF: most sensitive channel ‣ Boosted: associate jet production ‣ Systematics ‣ Data driven background estimations ~10% ‣ 𝜐 identification 5% and trigger 10% ‣ Lepton scale factors 2-3% � 4
H → 𝜐𝜐 OBSERVATION ‣ Combine results for all channels as a function of log 10 (S/(S+B)) ‣ Excess corresponding to 125 GeV particle ➞ Significance 4.9 σ ( 5.9 σ with 7 and 8 TeV measurement) +0.27 ‣ Signal strength of 1.09 -0.26 ➞ Compatible with SM ‣ Likelihood scan assuming M H =125.09 for k V and k f ‣ Contours compatible with SM hypothesis � 5
Phys. Lett. B 788 (2018) 7 HH → bb 𝛿𝛿 Selection ‣ ‣ 𝛿𝛿 trigger ‣ BSM theories foresee particles that couple to H pairs ‣ Jet and 𝛿 relative isolation ‣ Final state fully reconstructed , “big” branching ratio ‣ H( 𝛿𝛿 ) and H(bb) in mass window ‣ Both resonant and non-resonant searches ‣ Main background: n 𝛿 +jets Categories ‣ ‣ Sensitivity to non resonant searches ‣ MVA discrimination between H and n 𝛿 +jets ‣ Signal model: double Crystal-Ball ‣ Background model: n 𝛿 +jets (polynomials) and single H distributions � 6
HH → bb 𝛿𝛿 ‣ Systematics ‣ Photon energy resolution 5% ‣ No evidence of SM HH production ➞ Limits on cross section and branching ratio ‣ Jet energy resolution and scale 5% ‣ Exclusion of possible spin-0 and spin-2 particles ‣ Theoretical ‣ Upper limit on µ HH < 24 uncertainties 3-5% ‣ Limits on anomalous HHH coupling -11 < k λ < 17 � 7
F ROM LHC TO H IGH -L UMINOSITY LHC LHC HL-LHC ‣ Performances: Run I Run II Run III Run IV-V… ‣ Centre of mass energy 14 TeV 14 TeV 14 TeV 13 TeV LS1 LS2 LS3 ‣ Instantaneous luminosity from 8 TeV 5 to 7.5 x nominal 7 TeV luminosity 1.7 × 10 34 to 7.5 × 10 34 cm -2 s -1 2011 2012 2013 2014 2015 2016 2017 2018 2019 2020 2021 2022 2023 2024 2025 2026 2038 ‣ Goal: 3000 fb -1 integrated 2 x nominal 2.5 x nominal luminosity ➞ Huge statistics luminosity nominal luminosity 75% nominal luminosity luminosity ‣ Consequences: 30 fb -1 150 fb -1 300 fb -1 3000 fb -1 ‣ Huge crystal irradiation ➞ Loss of ~50% of barrel crystals’ transparency and small reduction of energy resolution (endcap crystals replaced by HGCAL) ‣ Substantial increase in pileup rate: from ~60 to 140-200 events/collision ‣ In order to maintain Phase-1 performances, need to: ‣ Reduce noise in photo detectors (Avalanche Photo-Diodes) due to LHC irradiation ➞ Cooling and new front-end pre-amplifier with shorter shaping time ‣ Perform precision time measurements to identify primary vertexes and reduce pileup contamination � 8
ECAL UPGRADE REPLACE ‣ Energy and time determination: sampling of shaped signal from photodetectors ➞ Upgrade of the very front-end, reduction of the shaping time KEEP ‣ Cooling system to reduce APDs dark current: from 18°C to 9°C ‣ Model the signal as a sum of one in-time pulse and a series of out-of-time pulses ‣ Remove out of time pileup ‣ Obtain time of arrival from template fit of pulse shape ‣ Test beam results: 30 ps resolution achievable for 25 GeV photons � 9
H → 𝛿𝛿 @ HL-LHC t 2 ‣ Photon energy resolution t 1 ‣ Exploit 3x3 crystal information to reduce pileup and noise contribution p-bunch p-bunch ‣ Vertex position ‣ Dominant with the increase of pileup ‣ 140 pileup ➞ 40% vertex reconstruction efficiency ‣ Solution: O(30 ps) time resolution allows better than 1 cm primary vertex determination ➞ Pileup contributions back to Run 2 levels arbitrary units -1 CMS 3000 fb (13 TeV) Projection → γ γ H S2 (80% Vertex Efficiency) fiducial volume : 1 1 gen γ p ( ) > ( ) m S2+ Optimistic (75% Vertex Efficiency) γ γ 3 4 T 1 (2) gen η γ | ( )| < 2.5 S2+ Intermediate (55% Vertex Efficiency) 1, 2 gen dummy0 dummy0 γ Iso ( ) < 10 GeV S2+ Pessimistic (40% Vertex Efficiency) R=0.3 1, 2 S/(S+B)-weighted σ S2 =1.71 GeV eff signal models 110 115 120 125 130 135 1 1.1 1.2 1.3 1.4 m (GeV) σ � 10 relative to S2 (GeV) γ γ eff
JINST 12 (2017) H → 𝜐𝜐 @ HL-LHC ‣ Fundamental Z → 𝜐𝜐 background rejection ➞ Excellent mass resolution required ‣ Same conditions of Run 2 achievable with upgrade ‣ Expected sensitivity on coupling modifier of 2-5% (30% in Run 2) HH → bb 𝛿𝛿 @ HL-LHC ‣ Expected significance 1.9 σ with 1000 fb -1 ‣ Improvements considering also 𝛿 background rejection with new ECAL timing performances ‣ M( 𝛿𝛿 ) allows separation between signal and non- resonant background, no H - HH discrimination � 11
S UMMARY ‣ Excellent results in Higgs searches in Run 2 (see also H → bb and coupling studies in general) ‣ Huge statistics needed to study rare processes such as HH production ➞ High-Luminosity LHC ‣ HL-LHC is a very challenging environment due to pileup and radiation condition ➞ Need an upgraded detector ‣ Precise timing and new electronics guarantee similar performances as those of Run 2 ‣ More precise analysis of single Higgs processes and study of rare multi-Higgs production are expected from simulations � 12
BACKUP � 13
T HE CMS EXPERIMENT � 14
A GEING PERSPECTIVES ‣ PbWO 4 crystals ‣ Transparency loss: ɣ radiation damages can be cured (annealing), hadron interactions produce permanent defects (shift in wavelength) ‣ Lower temperature operations (9°C vs 18°C) limit the annealing but increase the light output Avalanche Photo-Diodes ‣ Experience high dark current due to high level of LHC irradiation ➞ Worse energy resolution ‣ L ower operations’ temperature (9°C vs 18°C) strongly reduces dark current � 15
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